What is the universe made of?
Human understanding of the universe — how it works, its vastness and what it’s made of — has changed and grown, especially after humans began to apply mathematics, writing and new investigative principles. In the few hundred years since people began systematically investigating the nature of things, scientific principles and tools have been refined, and many of the mysteries of the universe have been revealed.
For example, scientists know that the universe is everything: all the matter and energy that space contains, even time itself. The universe comprises all the stars in all the galaxies and even things astronomers can’t observe yet. But simply knowing that the universe is everything isn’t enough to satisfy most people. We want specifics to precisely answer the question, “What is the universe made of?”
Breaking Down the Universe
Scientists typically like to break down the components of the universe into three categories: normal matter, dark matter and dark energy.
Normal matter consists of every visible object in the universe. This includes galaxies, star clusters, planets, dwarf planets, rogue planets, moons, rings, ringlets, comets, meteorites — every object in the universe and every bit of matter that makes up all the known elements in the periodic table, from black holes and massive stars to specks of space dust. All the types of normal matter obey the same natural laws, even though they exhibit different characteristics.
It’s believed that normal matter was created during the Big Bang. The early newborn universe was a heaving mass of neutrons, protons, electrons, photons and other subatomic particles that zipped around and smashed into one another forming hydrogen — the simplest and lightest atomic element, which is made of only a proton and an electron. Fourteen billion years later, individual hydrogen atoms remain the most common element found in the universe, making up nearly 95% of the universe’s atoms.
Helium is the second lightest and second most abundant element in the observable universe. According to NASA, close to 5% of the universe’s atoms are helium. All the rest of the elements in the periodic table make up a fraction of the remaining 1% of all ordinary matter in the universe.
Astronomers have also estimated the number of stars in the observable universe, starting with the Milky Way galaxy, which contains at least 100 billion stars. Since the observable universe contains at least 100 billion galaxies, this means there must be close to 10 sextillion (10,000,000,000,000,000,000,000) stars in the universe.
What About Dark Matter and Dark Energy?
But what about invisible matter? What about energy? For astrophysicists, dark matter and dark energy are the greatest mysteries and biggest challenges of the universe. Scientists label them as “dark” because they can’t directly observe them, which means most of the universe that can be known remains unknown. But the universe, as we understand it, wouldn’t work if dark matter and dark energy didn’t exist.
If all the normal matter — the stars, planets, comets and everything else we can observe — represents less than 5% of what the universe is made of, then about 27% of the remainder is dark matter, and 68% is dark energy, neither of which is even remotely understood. But there’s still hope. In the early 21st century, astronomers discovered thousands of planets around other stars, detected gravitational waves for the first time and produced the first image of a black hole. We’re learning more about these mysteries of the universe every day.
While dark matter can’t be observed directly yet, its fingerprints are preserved in the universe’s first light as tiny fluctuations in radiation. We can investigate some of the properties of dark matter using gravitational lensing, a process that measures how much the dark matter causes light from a background source to bend. NASA’s Chandra X-Ray Observatory and optical telescopes use gravitational lensing to help map the distribution of dark matter in colliding galaxy clusters.
By using the gravitational lensing technique, astronomers can get an idea of the galaxy’s mass and measure how much the dark matter bends the light. When the mass we calculate from the bend and the mass we can observe directly don’t agree, we know dark matter must be present. The warping and magnification of this light give us insight into the amount, density and distribution of dark matter in any given lensing galaxy. Astrophysicists have calculated that dark matter — even though it can’t be seen or measured — must make up a significant portion of the universe.
The Even More Mysterious Part of the Universe
Even stranger than dark matter, though, is dark energy, which is thought to be more abundant than either matter or dark matter. Dark energy is the unseen repellant force required to explain the expansion of the universe, which should be slowing down because of the gravitational attraction between galaxies. Models of the force required to explain the universe’s accelerating expansion rate suggest that dark energy must make up about 68% of the universe.
The Chandra Observatory has placed limits on dark energy by looking for its effects on galaxy cluster evolution throughout the history of the universe. By comparing observations of galaxy clusters with experimental models, researchers are studying how dark energy competed with gravity throughout the history of the universe. Considering that dark energy makes up about three-quarters of the universe, understanding it is one of the most significant challenges facing scientists today.
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